Many types of power turf mowing equipment are known. Such equipment can be classified into those mowers which include a rotary cutting unit(s) and those which include reel cutting unit(s). A rotary cutting unit usually includes one or more rigid steel blades rotated within a housing in horizontal cutting planes to sever grass or other vegetation at a predetermined height above the ground. Turf mowers having rotary cutting units are often referred to as rotary mowers since the blades revolve in a rotary fashion within the cutting unit.
A reel cutting unit, on the other hand, typically includes a frame within which is horizontally rotatably mounted a reel possessing a plurality of arcuate blades. The rotating reel blades pass in close proximity to a bedknife which spans the cutting unit frame parallel to the reel axis. Grass blades are sheared at the reel blade/bedknife interface.
While rotary cutting units are generally suitable for most purposes, it is generally perceived that reel units provide a higher quality cut. Also, it is fairly easy to arrange a plurality (typically three, five or seven of reel cutting units into a "gang" capable of cutting a very wide swath each pass. In turf mowing machines of the type known as gang mowers, several cutting units are held in spaced positions in transverse rows of one or more units so that their swaths overlap and so that the units are individually free to adapt themselves to the undulations of the ground.
Power turf mowing equipment can also be categorized based on the method of propelling the cutting units. Generally, there are walk-behind; riding; and towed cutting unit mowers. The present invention relates to the latter two types; walk-behind mowers are usually found in residential settings, and the present invention does not pertain to such mowers.
Larger riding mowers typically include a traction vehicle supported by a plurality of wheels; a prime mover connected through a transmission to one or more of the wheels; one or more cutting units connected through a power take-off (PTO) to the prime mower; and one or more lift arms (or analogous structures) pivotally connected to the traction vehicle suitable for supporting the cutting unit(s).
Towed cutting units would normally include a towable frame suitable for connecting to a tractor or other traction vehicle. Suspended from the towable frame would usually be several cutting units, the power for the cutting units being derived either from a PTO or the traction vehicle's prime mover; a separate prime mover mounted on the towable frame; or from frictional engagement with the ground as the cutting units are pulled along.
The present invention relates to riding mowers and towable mowing frames having reel cutting units. As is well known, another reel-like unit is used to produce a "verticut," and this type of cutting unit is also contemplated. For the sake of brevity, the invention will hereafter be discussed in terms of large commercial riding mowers.
Experience has shown that it is very advantageous to connect the reel units to the traction vehicle such that they can "float" relative to the traction vehicle. A "floating" reel unit can follow the contours or undulations of the ground irrespective of the gross motion of the traction vehicle. If reel units are not supported in a floating manner, they tend to scalp the higher regions and miss the lower regions. While non-floating cutting reels might be acceptable for residential use, certainly golf course and estate maintenance require that the cutting units individually follow the subtle variations of the ground to maintain a consistently good cut across the entire swath, regardless of the immediate topography encountered by each individual reel unit.
In this type of mower each reel unit is independently and separately pivotally supported by the traction vehicle, and each reel unit is typically driven by a mechanical or hydraulic drive extending from the traction unit to the reel unit. An example of this type of mowing machine is the 350D mower sold by the Toro Company, assignee herein.
The method by which the reel units are attached to the traction vehicle is important not only because the reel units must float to provide a quality cut, but also for other reasons. For example, the connection between the reel units and the traction vehicle must permit, if not assist, lifting of the reel units from their operative positions to their transport positions. The operator might want to temporarily raise one or more of the cutting units to mow a narrower swath or to pass through a gate or between trees. Also, it is occasionally necessary to drive the mowing machines over conventional road surfaces, at which time it is important to raise the cutting units to a transport position since they are not entirely suitable for repeatedly running up and down over curbs, nor for travel over paved streets at anything approaching the speed of ordinary city traffic. In view of this, most riding mowers, such as the one described in U.S. Pat. No. 2,299,859, include mechanisms which can raise the cutting units upward and toward the traction vehicle into a substantially vertical orientation.
When a reel unit is in its raised or transport position, it must be held there very securely. Otherwise, it may tend to swing and thereby cause personal injury or damage to the mower. Also, if the connection between the traction vehicle and the reel units is inadequate, when the reel units are lowered they may contact the ground in a tilted or skewed state, and this can cause a hole or undesirable compaction in the ground.
The means for supporting the reel units must therefore allow for limited floating of the reel units; permit controlled lifting of the reel units for transportation purposes; and precisely hold the reel units in their raised or transport position. The joint or connection means between the cutting units and the traction vehicle must also be quite rugged; simple and easy to maintain; relatively inexpensive; and relatively light (so as not to overburden the traction vehicle).
Against the background of the afore-mentioned criteria, various reel unit support methods have been suggested. These support techniques can be generally categorized according to the number of degrees of freedom which they afford the cutting units. FIGS. 1-4 show various prior art reel unit supporting systems. It should be noted that FIGS. 1-4 are not intended to represent structures which are precisely found in the prior art, but are instead provided to illustrate prior art reel support concepts. For example, the structure shown in U.S. Pat. No. 1,556,965 allows for vertical displacement and "yaw" whereas FIG. 2 shows very diagrammatically a structure which allows for vertical displacement and "roll" of a cutting unit, but both systems may be termed "two-degree-of-freedom" support techniques in that they allow the reel to move in two distinct and independent ways relative to the traction vehicle or support frame. The terms "roll" and "yaw" are defined below. As another example, the structure shown in FIG. 1 is meant to represent systems such as the one depicted in U.S. Pat. No. 2,525,047. The system shown in this patent includes reel units which have only one-degree-of-freedom, namely "roll" with respect to a towed frame. Similarly, FIG. 3 is provided simply to help categorize the prior art, and no representation is made that the diagrammatic structure shown in FIG. 3 is actually found in its entirety in prior art structures. In fact, ball joints in combination with a "lift arm" per se may not be found at all in the prior art. The labels "Prior Art" on FIGS. 1-4 are attached only to distinguish these figures from FIGS. 5-8 which show the present invention.
FIG. 1 illustrates a very simple prior art support concept wherein a reel unit is rigidly attached to a lift arm or the like which in turn is pivotally connected to a traction vehicle. A structure employing this concept is shown in U.S. Pat. No. 2,525,047, as noted above. This system allows only "rolling" (to borrow a term from the aviation field) of a cutting unit relative to the main traction vehicle, and it can be termed a "one-degree-of-freedom" method since the cutting unit can only move pivotally in one direction. While this mounting scheme is inexpensive and lends itself to easily and securely raising the cutting units to their transport positions, it is clearly disadvantageous from the standpoint of allowing the cutting units to follow the contours of the ground independent of the traction vehicle.
FIG. 2 diagrammatically illustrates a simple "two-degree-of-freedom" reel unit supporting technique. Here, as was the case with the one-degree-of-freedom system discussed above, the reel unit can move or pivot vertically relative to the traction vehicle. In addition, the reel unit of the FIG. 2 system can tip from side-to-side relative to the lift arm, there usually being a simple bushing or the like at their connection point. An example of this type of system is shown and described in U.S. Pat. No. 3,613,337. This technique allows for vertical displacement and "roll" of the cutting unit, again borrowing terminology from the aviation field to describe the motion of the cutting unit. Thus, the cutting units can roll to follow subtle ground undulations.
The system shown in FIG. 2 is also desirable from the standpoint that the cutting units can be securely lifted to a transport position. The joint between the lift arm and the reel unit allows for only limited motion of the reel unit, which means that the reel unit is quite controllable and predictable during the raising and lowering sequences.
Although the two-degree-of-freedom system shown in FIG. 2 is theoretically superior to the one-degree-of-freedom system shown in FIG. 1 in that it allows the cutting unit to more closely follow the undulations of the ground, this technique still does not allow for "pitching" (as in the pitching forward or rearward of an airplane) of the reel unit.
In view of the desirability of still greater floating action (i.e., "pitch") of cutting units relative to the lift arms, ball-and-socket joints have been proposed for use between lift arms (or the like) and cutting units. Ball joints, as is well known, allow almost unlimited rotary or spherical motion, and therefore would seem to offer a simple solution to the floating problem. FIGS. 4A, 4B and 4C show a few of many degrees of freedom allowed by a ball joint between a lift arm and a cutting unit. As shown, ball joints allow for vertical displacement (FIG. 3A), "pitch" (FIG. 3B), "roll" (FIG. 3A) and "yaw" (FIG. 3C). While it might seem, at first glance, desirable to allow for yaw of a cutting reel unit, the present Applicants have found that yaw is generally unnecessary and in fact should often be avoided in the context of riding mowers, for several reasons. For one thing, it is desirable to have a single lift arm or the like connected to a reel unit which can propel the reel unit and also selectively lift the reel unit. If yaw is allowed, there must generally be two separate pull and pick up devices or arms. The assignee herein markets a power turf maintenance apparatus under the designation PARKMASTER.RTM. which includes separate pull and pick up mechanisms, and although the system works well, it is perceived that it can be improved upon.
Also, if reel units are allowed to yaw, the inner cutting units may strike their respective lift arms during a sharp turn. Of course, stops could be built into the system to prevent this from happening, but it presents an unnecessary complication nonetheless.
Finally, if reel units can yaw relative to their traction vehicle, it is more difficult to tilt them upwards during the reel lifting operation. Reel units usually include a tipper bracket or the like which strikes a roller mounted on the traction vehicle to tilt the reel unit vertically as the lift arm pivots upward. If the reel units were allowed to yaw, the tipper brackets and/or rollers would have to be considerably wider to account for the fact that the reel units could be "yawed" to either extreme at the commencement of the lifting sequence.
Whether or not reel unit yawing is deemed desirable, ball joints between lift arms and cutting units are generally unsatisfactory: (i) ball joints do not include roller-type bearings, i.e., ball bearings or needle bearings; (ii) they are not adequately sealed; (iii) they are generally not rugged enough for this application; and (iv) it would be difficult to "lock out" or prevent pitching of the cutting units when necessary. In a dethatching operation, for example, it is desirable to allow rolling of the reel unit while preventing reel unit pitching.
Moreover, the use of ball joints between the reel units and the traction vehicle also usually necessitates use of additional stabilizer links to eliminate some of the freedom of motion afforded by the ball joints. Reference is made to U.S. Pat. Nos. 2,505,878 and 2,475,671 which show such situations.
Still another support technique for a reel unit can be termed a "three-degree-of-freedom" scheme. FIG. 4 diagrammatically shows two three-degree-of-freedom systems. FIG. 4A shows a simple "stacked bushing" technique wherein two orthogonal bushings are in effect stacked to provide pitch and roll. This type of system is evident in the Ransomes' mower Model No. 350D, shown in their Publication No. 23135H. A conceptually similar design is shown in FIG. 4B, but in this case there are actually three bushings: a central upper bushing permits roll of the cutting unit whereas two axially-aligned end bushings connected to the side plates of the reel unit allow for pitching of the reel unit relative to the lift arm. The Toro Company, the assignee herein, sells a REELMASTER.RTM. 216 mower which has this type of reel unit suspension. While the designs shown in FIGS. 4A and 4B are advantageous in that they eliminate bothersome yaw, as a class they each have theoretical disadvantages. For the stacked bushing design diagrammatically shown in FIG. 4A, the roll bushing is displaced from the reel center line to such an extent that a fairly long moment arm is created between the roll bushing and the center line of the cutting reel sufficient to create a significant twisting moment on the lift arm during normal operation and when obstructions are encountered. Further, with this design it is somewhat cumbersome to lock out reel pitching. As shown in the Ransomes brochure referred to above, the roll bushing pivots within a U-shaped bracket mounted to the reel unit frame. To lock out pitch of the reel, the roll bushing must be somehow rigidly connected to the U-bracket.
The type of system shown in FIG. 4B also has disadvantages, the obvious one being that there are three bushings to maintain. Bushings, as a class, are notoriously sensitive to sand and grit, substances found in abundance on golf courses and the like. Also, many bushings are simply not well suited for the very heavy loads to which reel cutting units on commercial turf maintenance machines are subjected. Further, many bushing joints are not sufficiently smooth or friction-free to allow for free floating of reel units. If binding of a reel unit occurs when it is lowered from the transport position to the operation position, the cutting unit can potentially cause an undesirable hole or compaction in the turf.
The present invention addresses the problems possessed by prior art reel unit suspension systems. In particular, the present invention includes a three-degree-of-freedom reel supporting system which allows for adequate "floating" of the reel unit; accommodates existing reel unit lifting techniques; and is rugged, inexpensive, and compact.